The cause of the problem has to do with how grid variables are named. For a radio button grid, we use variable names like "S5_r1" or "S5_c2" because that is all that is required to identify which part of the grid question we're talking about. But for all other types of grid questions, that naming convention doesn't hold up. For a numeric grid question, does "S5_r1" refer to the input on the first row and first column or the input on the first row and second column? This is why the software requires that non-radio type grids be defined with their row number and column number, even in the case where the grid only has one row / one column.
S5_r2_c1 < 25